Removing duplicate elements from an array in Swift

Question

I might have an array that looks like the following:

[1, 4, 2, 2, 6, 24, 15, 2, 60, 15, 6]

Or, reall

Answer 1

In case you need values sorted, this works (Swift 4)

let sortedValues = Array(Set(array)).sorted()

Answer 2

Swift 5

extension Sequence where Element: Hashable {
    func unique() -> [Element] {
        NSOrderedSet(array: self as! [Any]).array as! [Element]
    }
}

Answer 3

You can use directly a set collection to remove duplicate, then cast it back to an array

var myArray = [1, 4, 2, 2, 6, 24, 15, 2, 60, 15, 6]
var mySet = Set<Int>(myArray)

myArray = Array(mySet) // [2, 4, 60, 6, 15, 24, 1]

Then you can order your array as you want

myArray.sort{$0 < $1} // [1, 2, 4, 6, 15, 24, 60]

Answer 4

edit/update Swift 4 or later

We can also extend RangeReplaceableCollection protocol to allow it to be used with StringProtocol types as well:

extension RangeReplaceableCollection where Element: Hashable {
    var orderedSet: Self {
        var set = Set<Element>()
        return filter { set.insert($0).inserted }
    }
    mutating func removeDuplicates() {
        var set = Set<Element>()
        removeAll { !set.insert($0).inserted }
    }
}

---

let integers = [1, 4, 2, 2, 6, 24, 15, 2, 60, 15, 6]
let integersOrderedSet = integers.orderedSet // [1, 4, 2, 6, 24, 15, 60]

---

"abcdefabcghi".orderedSet  // "abcdefghi"
"abcdefabcghi".dropFirst(3).orderedSet // "defabcghi"

---

Mutating method:

var string = "abcdefabcghi"
string.removeDuplicates() 
string  //  "abcdefghi"

var substring = "abcdefabcdefghi".dropFirst(3)  // "defabcdefghi"
substring.removeDuplicates()
substring   // "defabcghi"

---

For Swift 3 click here

Answer 5

You can roll your own, e.g. like this:

func uniq<S : Sequence, T : Hashable>(source: S) -> [T] where S.Iterator.Element == T {
    var buffer = [T]()
    var added = Set<T>()
    for elem in source {
        if !added.contains(elem) {
            buffer.append(elem)
            added.insert(elem)
        }
    }
    return buffer
}

let vals = [1, 4, 2, 2, 6, 24, 15, 2, 60, 15, 6]
let uniqueVals = uniq(vals) // [1, 4, 2, 6, 24, 15, 60]

And as an extension for Array:

extension Array where Element: Hashable {
    var uniques: Array {
        var buffer = Array()
        var added = Set<Element>()
        for elem in self {
            if !added.contains(elem) {
                buffer.append(elem)
                added.insert(elem)
            }
        }
        return buffer
    }
}

Answer 6

Swift 4

public extension Array where Element: Hashable {
    func uniqued() -> [Element] {
        var seen = Set<Element>()
        return filter{ seen.insert($0).inserted }
    }
}

---

every attempt to insert will also return a tuple: (inserted: Bool, memberAfterInsert: Set.Element). See documentation.

Using the returned value helps us to avoid looping or doing any other operation.